Railroad tie
|
A variant fastening of rails to wooden sleepers |
A
railroad tie, cross tie, or
sleeper is a rectangular object used as a base for
railroad tracks. Traditionally, ties have been made of
wood, often heavily
creosoted or, less often, treated with other
preservatives (for more information on wood preservatives see
lumber), but
steel has also been used and
concrete is now widely used.
Ties are laid on top of
sand,
gravel or heavy crushed
stone - called
track ballast. They are laid across the grade at intervals of about two feet. The steel rails are then laid atop the ties, perpendicular to them. If the ties are wood, then cleats are laid down and spikes driven through them into the ties to clamp down the rails. The rails are held on wooden ties with
rail spikes. For concrete ties,
steel clips (for example the
Pandrol clip) are often used to fasten the rails. After this is done, additional ballast is then added to fill the spaces between and around the ties to anchor them in place.
The ties then act as anchors and spacers for the rails, while providing a slight amount of give to accommodate weather and settling. The ties are "floating" in the top of the ballast. Failure of a single tie is generally insignificant to the usability and safety of the rails. A
datenail was implemented and coded by the railroads to identify the age of the railroad tie (that was usually laid down in sections) by hammering it into the railroad tie after installation for maintenance purposes. A typical
mile of rail contains approximately 3,000 ties.
In recent years, wooden railroad ties have also become very popular for
gardening and
landscaping, both in creating
retaining walls and raised-bed gardens, and sometimes for building steps as well. Traditionally, the ties sold for this purpose are old ones taken from rail lines when replaced with new ties, and their lifespan is often limited due to rot. Some entrepreneurs sell new ties. Unfortunately, due to presence of wood
preservatives such as
coal tar,
creosote or
salts of
heavy metals, railroad ties introduce an extra element of
soil pollution into gardens and are avoided by many
property owners. In the
UK, new
oak beams of the same size as standard railroad ties, but not treated with dangerous chemicals, are now available specifically for garden construction. They are about twice the price of the recycled product. In certain places, railroad ties have been used in the construction of homes, particularly among those with lower incomes, especially those residing near railroad tracks, including railroad employees.
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Koppers
